The present invention is generally concerned with drive mechanisms for operating rotary printing structures, and more particularly with an improved drive system for intermittently operating rotary printing structures.
As shown in U.S. Pat. No. 2,934,009, issued Apr. 26, 1962, Bach, et al. and assigned to the assignee of the present invention, there is described a mailing machine which includes a postage meter and a base on which the postage meter is removably mounted. The postage meter includes a rotary printing drum and a drive gear therefor which are mounted on a common shaft and normally located in a home position. In addition, the postage meter includes a shutter bar movable into and out of locking engagement with the drive gear. The base includes a drive mechanism having an output gear which is disposed in meshing engagement with the drum drive gear, and includes a shutter bar lever arm disposed in engagement with the shutter bar when the postage meter is mounted on the base. The drive mechanism includes a single revolution clutch, having a helical spring, for actuating the shutter bar lever arm, to move the shutter bar out of locking engagement with the drive gear, and for rotating the gear and thus the drum from its home position and into engagement with a sheet fed to the drum. Each revolution of the clutch, and thus of the drum, is initiated by a sheet engaging a trip lever to release the helical spring. In the course of each drum revolution, the drum prints a postage value on the sheet while feeding the same downstream beneath the drum as the drive mechanism returns drum to its home position and causes the shutter bar to be moved into locking relationship with the drive gear. Thus the driving mechanism intermittently operates the rotary printing drum.
Although the single revolution clutch structure has served as the workhorse of the mailing machine industry for many years, it has long been recognized that it is a complex mechanism which is relatively expensive to construct and maintain, tends to be unreliable in high volume applications, and is noisy and thus irritating to customers.
Accordingly, an object of the invention is to replace the drive mechanism of the prior art with a simplified, highly reliable and quietly operating drive system including means for controlling the shutter bar.